1. Field of the Invention
This invention relates generally to a circuit board test fixture. More specifically, it concerns a vacuum operated fixture having a flexible diaphragm for moving a circuit board into testing engagement with electrical probes.
2. Description of the Prior Art
Known vacuum operated test fixtures require extensive disassembly for removal of a diaphragm and a backing plate from the fixture top to replace or clean probes. Removing screws, stripping retainers, and then replacing the retainers and screws can be time consuming. A tester requiring screw and retainer removal before diaphragm and plate removal is disclosed in U.S. Pat. No. 4,017,793 of Fred E. Haines. This patent also discloses a vacuum chamber base member that is adapted to be pivoted upwardly for easy working with electrical contacts and other parts within a dust cover. When elastomeric foam is used for a diaphragm, it should not be bent sharply or compressed as to disfigure the foam. Such bending and compression causes excessive wear, deterioration of the foam and susceptibility to tear. Thus, the diaphragm should be maintained with minimal stress, but must form an air-tight seal at the fixture top for maintaining a pressure differential on opposite sides of the diaphragm.
Back-up plates have been sealed between a diaphragm and a head plate by cementing the peripheral edges of the diaphragm to the head plate. A rectangular frame fits about the peripheral edges of the diaphragm, and the frame and the head plate fit within guide rails. Such structure is disclosed in U.S. Pat. No. 4,138,186 of Everett J. Long, et al. This patent also discloses, as prior art, an arrangement wherein the peripheral edges of a sealing member fit within slots in a picture frame shaped housing. An inclined sealing surface at the bottom of the slot is engaged by the sealing member when a vacuum chamber is evacuated. An upper flange, defining the top of the slot, overlaps both the sealing member and a backing member, making removal of the backing member difficult.
A test jig for contacting circuit card positions is disclosed in U.S. Pat. No. 3,016,489 of T. H. Briggs, et al. A flexible diaphragm element that is fastened within a housing is located beneath peg-like plungers or pins. Air or hydraulic pressure forces the diaphragm upward to contact the plungers or pins, forcing probe assemblies into contact with the circuit card. Mounting channels receive the circuit card that is clamped therein by a top mounting channel molding clamp. Other circuit board test equipment is disclosed in U.S. Pat. No. 3,757,219 of Akin Aksu, U.S. Pat. No. 3,714,572 of Jack Wesley Ham, et al., and British patent specification No. 1,297,377 of Edwin Albert Quincey, et al.